Counter-battery radars are used to track incoming artillery shells or mortar rounds. The target radar cross section (RCS) of an artillery shell or a mortar round is usually in the range of -22 dBsm (square meter) to -40 dBsm. An aircraft which has an RCS between +14 dBsm and -10 dBsm can fall in the sidelobe region of the radar antenna and produce a signal strength similar to a true artillery shell or mortar round target tracked by the main beam monopulse. In several field tests where aircraft and artillery shells co-exist, aircraft have been falsely tracked by the sidelobe monopulse and mistaken as an artillery shell because the -30 dB to -50 dB sidelobe level suppresses the aircraft RCS to the size of an artillery shell RCS. Since the aircraft is tracked in the sidelobe region the angular error is usually large.
To address this problem, sidelobe blanking systems have been employed which utilize a low-gain omnidirectional antenna operating in conjunction with the sum beam. Signals from both antennas are fed to separate receivers and their outputs compared. Any comparisons showing greater power level in the low gain channel are canceled, thus eliminating returns from those sectors of the sum beam having gain levels less than the omnidirectional antenna. A gain control in the omnidirectional antenna channel is required for adjusting the degree of sidelobe blanking.
The disadvantages of the sidelobe blanking system are: (1) it requires an additional omnidirectional antenna and a receiver channel, (2) gain control between the receiver channels has to be checked periodically to ensure no faulty results due to receiver gain variation over time, and (3) additional antenna and receiver hardware are difficult to fit to the existing form factor and radar platform. This invention eliminates these disadvantages.